Speed of Light, measured tonight…
Well, I was bored, and it was getting close to midnight. There was nothing really going on on any of the amateur radio bands, so I got to thinking. Light travels about 186,000 miles per second, or about 186 miles per ms. On 10Mhz, NIST broadcasts a standard time signal from stations in Colorado, and in Hawaii. A little Wikipedia work told me that they are located:
CM87ux -> BL01cx: bearing 254.4°, distance 2479.3 miles (to Boulder) CM87ux -> DN80xq: bearing 73.8°, distance 1095.7 miles (to Hawaii)
The difference is about 7.44ms. So, I recorded some of the time signal tonight, where I could hear both signals. The start of the minute is indicated by a 1000 hz signal from Boulder and a 1200 Hz signal from Hawaii. Here’s the spectrogram I came up with:
Click on it to see the enlarged picture. Each horizontal pixel is 1ms. Sure enough, you can see that the lower frequency path is about 7 pixels to the left of the upper trace. Physics confirmed!
(Yes, there are better ways to detect the start of each pulse, this is just what I had on hand. Glad to see it worked though.)